This research project is focused primarily on two aspects of preimplantation development in the mammal: (1) The relative roles of maternal and embryonic gene products in supporting development during the immediate post-fertilization period; and (2) The principal signals by means of which the growing blastocyst and the uterus can and do communicate. The role of maternal gene products in early embryonic development will be investigated by continuing a study on RNA and protein synthesis during oocyte maturation. High-resolution, two-dimensional polyacrylamide gel electrophoresis will be used to study the qualitative aspects of protein synthesis during oocyte maturation as well as during early embryogenesis. The RNA polymerase inhibitor alpha-amanitin will be used to assess the role of the initial embryonic gene products in development. The signaling which occurs between blastocyst and uterus can result in growth control in the former and decidualization in the latter. Growth control in the blastocyst will be examined primarily in the mouse embryo, which is capable of prolonged periods of diapause. In vitro conditions have been established which closely mimic the diapause which occurs in vivo. The sequence of ultrastructural and metabolic events which accompany reactivation of the blastocyst will be studied. Decidualization will be investigated by attempting to identify the enbryonic synthesis of materials with relevant biological activity, such as steroids and prostaglandins. The role of small molecules, such as ions, in regulating protein synthesis in blastocyst will also be examined.